1. Field of the Invention
The present invention relates to an absorption type gas analyzer using infrared rays, ultraviolet rays and the like.
2. Description of the Prior Art
In an absorption type gas analyzer, for example an infrared gas analyzer, the absorption of infrared rays incident upon the inside of a cell from a light source by a sample gas contained in the cell is measured to determine the concentration of an ingredient gas contained in the sample gas. This absorption type gas analyzer is fundamentally based on Lambert-Beer's law. That is to say, provided that an intensity of the incident ray is I.sub.o, in a cell having a length l, an absorptivity constant K (the constant determined by a measuring-wave length and an object to be measured), and a gas-concentration being C, the intensity of the transmitted ray I is expressed by the following equation: EQU I=I.sub.o e.sup.-KCl
Accordingly, in an absorption gas type analyzer, the relation between the concentration of an ingredient gas to be measured and the output of the transmitted light has a larger curvature with an increase of the concentration of an ingredient gas to be measured, as shown in FIG. 2. In order to improve the accuracy of measurement by using an almost linear portion of the curve shown in FIG. 2, the cell length is reduced when the concentration of an ingredient gas to be measured is high while the cell length is increased when the concentration of an ingredient gas to be measured is low.
A prior art absorption analyzer, in which the cell length is changed in correspondence with the concentration of an ingredient gas to be measured in a sample gas, is disclosed in for example Japanese Utility Model Publication No. 49-25349. In such a prior art device a plurality of cells are arranged in series between a light source and a detector and the cells to be used are changed in correspondence to the cocentration of the ingredient gas to be measured in a sample gas.
However, this prior art device has exhibited disadvantages in that since the cells are arranged in series, the analyzer must be large-sized and overly long as a whole, and a troublesome operation is required in order to change the cell-length in correspondence to the concentration of the ingredient gas to be measured. In addition, although the provision of an interference filter sideways a light source is disclosed in the above-described Japanese Patent Publication, merely an influence of an interference spectrum upon the measurement is eliminated by previously removing an interference spectrum band overlapping on an absorption spectrum band of an ingredient gas to be measured, but other effects are not achieved.